1. Field of the Invention
This invention relates to gelatin capsules and fill materials therefore. More specifically, the invention relates to gelatin capsules and fill materials suitable therefore where the fill materials contain polyethylene glycol and dye, pigment, or various cosmetic materials. It further relates to methods for preparing such fill materials and gelatin capsules.
2. Description of Related Art
Soft gelatin capsules (softgels) have been employed for the efficient and convenient delivery of a variety of substances for numerous different uses. For example, cosmetics, pharmaceuticals, and dyes or pigments have been encapsulated into soft gelatin capsules.
A specific use for dye-filled soft gelatin capsules is as paint-filled gelatin capsules, i.e., paintballs. Paint-filled softgels have found use as markers for trees (see U.S. Pat. No. 3,861,943) and as target shooting capsules for use with air powered rifles or handguns (see U.S. Pat. No. 4,656,092).
Conventional technology for manufacturing paintballs relies on the use of high molecular weight polyethylene glycols (PEG) as a thickener for the fill composition containing the dye. However, the use of such PEGs in paintballs is undesirable since it adds processing steps and the need for heat to melt the PEG thickener. For use in paintballs and other gelatin capsules as a component of the fill material, high molecular weight PEG must be melted and subsequently combined while hot with the remaining fill components. The resulting hot fill material must be cooled slowly and carefully, generally over a period of about 48 hours. Hot fill material cannot be used to fill soft gelatin capsules made with the rotary die process; gelatin capsules made with hot fill material have various problems including the lack of good seals since the addition of the fill is essentially concurrent with seal formation. Moreover, imprecise cooling typically results in defective fill material product.
The heating process is unattractive since it demands long processing times and large amounts of energy. In addition, the resulting products are generally suitable for use in limited temperature ranges since the high molecular weight PEG loses its ability to act a thickener at low temperatures and nearly solidifies at low temperatures. The proper stability of the fill material is necessary to produce a capsule projectile that will have a reliable trajectory upon being shot.
High molecular weight PEG also results in capsule projectiles that tend to increase size at low temperature as the fill materials, which typically include water, freeze. The resulting projectiles cause damage of the guns used to shoot the capsules, an obvious problem which can also injure the user of the gun.
Consequently, there is a need for fill materials suitable for use in gelatin capsules that are also capable of carrying a pigment where the fill material is not based on a high molecular weight polyethylene glycol. Suitable fill material compositions must be such that they (1) maintain their uniform character after filling into gelatin capsules and (2) are liquid at low temperature. In other words, the compositions must not separate at ambient temperature and not become too hard at temperatures near or below freezing.
U.S. Pat. No. 4,656,092, the disclosure of which is incorporated herein in its entirety, discloses target shooting capsules comprising a substantially spherical, nontoxic, soft elastic gelatin capsule containing a water washable, nontoxic fill material.